The present invention relates generally to vehicle adaptive cruise control systems, and more particularly to a method and apparatus for adjusting vehicle speed and maintaining a headway distance in response to a target.
Adaptive Cruise Control (ACC) has reached a level of technical and business readiness such that it is beginning to appear in the consumer market as a comfort and convenience system. Consumer technical enthusiasm for ACC has increased because of their interest in intelligent vehicles and systems such as collision warning and collision avoidance. ACC performs as an enhancement to traditional cruise control by automatically adjusting a set speed, which is set by the vehicle operator, to allow a vehicle to adapt to moving traffic.
Under normal driving conditions the ACC system is engaged with a set speed equal to a maximum autonomous speed that is desired by the operator and the ACC system operates in a conventional cruise control mode. When the vehicle approaches traffic, the ACC system automatically adjusts the set speed to follow the traffic at a desired headway distance. When the traffic clears, the ACC system slowly resumes the speed of the vehicle to the set speed. When the ACC vehicle performs a lane change, and the actual distance to a new target is less than the set headway distance, the ACC vehicle will remain in follow mode. When the vehicle approaches slow traffic, whereby the ACC system determines to reduce speed of the vehicle below a minimum speed for ACC operation, the ACC system is automatically disengaged and the operator manually follows slower vehicles in the slow traffic. When the slow traffic is no longer in front of the vehicle the operator must manually accelerate the vehicle to a velocity above the minimum speed for ACC operation, approximately 40 KPH, before the ACC system is able to resume acceleration to the set speed by depression of a resume button.
During slower stop and go traffic the operator frequently adjusts the speed of the vehicle by applying the brakes or depressing the accelerator. The continuous adjusting of the vehicle speed can become frustrating for the operator over extended periods of time.
Traditional ACC systems were designed to only react to moving targets presented by normal traffic under extended cruise control operation and when the vehicle is traveling at velocities above 40 KPH. Therefore, by operating only when certain conditions exist, the ACC system is compromising the goals of a collision warning or avoidance system.
It would therefore be desirable to develop an ACC system that operates at vehicle speeds below 40 KPH. It would also be desirable for the ACC system to correctly classify targets when traveling at the slower speeds. The ability to operate and classify targets at slower speeds may increase the success of ACC systems in the consumer market and also increase the collision warning capabilities of a vehicle.
The foregoing and other advantages are provided by a method and apparatus for adjusting vehicle speed and maintaining a headway distance in response to a target. An ACC system includes a forward-looking sensor generating a range signal corresponding to a distance between the host vehicle and a target vehicle. The forward-looking sensor also generates a range rate signal corresponding to a rate that the distance between the host vehicle and the target vehicle is changing. A controller is electrically coupled to the forward-looking sensor. The controller maintains a preset headway distance between the host vehicle and the target vehicle by adjusting the host vehicle velocity in response to the range signal and the range rate signal. The host vehicle may come to a full stop when the target vehicle is acquired below a predetermined velocity. If the target vehicle is acquired above the predetermined velocity, then a warning is given when braking is required.
The present invention itself, together with attendant advantages, will be best understood by reference to the following detailed description, taken in conjunction with the accompanying figures.